A method for improving the agglomeration of silica powder

Abstract

The present invention discloses a method for improving the agglomeration of silica powder, comprising the following steps: (1) preparing a mixed slurry containing silica raw powder and carbon black; (2) spray-drying the mixed slurry; (3) calcining the powder obtained in step (2) at a high temperature in nitrogen and then cooling it; (4) performing low-temperature carbon removal calcination on the powder obtained in step (3) in air; (5) dispersing the powder obtained in step (4) to obtain a monodisperse and high true density silica powder. The present invention uses carbon black as a barrier substance to prevent powder agglomeration during the sintering process, thereby obtaining monodisperse submicron spherical silica powder.

Description

Technical Field

[0001] The present invention belongs to the technical field of silica production, and particularly relates to a method for improving the agglomeration of silica powder synthesized by a chemical method. Background Art

[0002] Spherical silica powder has excellent properties such as low dielectric constant, high heat resistance, high moisture resistance, high filling amount, and low impurities. It is used in fields such as electronic packaging materials EMC and CCL, which can greatly improve the wear resistance, impact resistance, compressive resistance, tensile resistance, flame retardancy, arc resistance insulation, and ultraviolet radiation resistance of materials. With the rise of the semiconductor industry and the rapid development of large-scale integrated circuits, higher requirements are put forward for the purity, particle size, density, and sphericity of spherical silica powder.

[0003] At present, the methods for preparing spherical silica powder mainly include physical methods and chemical methods. The physical methods mainly include flame spheroidization method, high-temperature melting spraying method, and plasma method. The chemical methods mainly include gas-phase method, hydrothermal synthesis method, sol-gel method, and microemulsion method. Among them, the sol-gel method is a method in which metal organic or inorganic compounds are solidified through solution, sol, and gel, and then heat-treated to form oxides or other compound solids. The SiO 2 powder prepared by the sol-gel method has high purity and narrow particle size distribution. In particular, it can synthesize spherical powder with particle size in the sub-micron range, and has advantages that other chemical or physical methods do not have. However, the SiO 2 prepared by the sol-gel method contains a large amount of hydroxyl groups, and the powder is not dense enough. It needs to be calcined at high temperature to make it densified. Although high-temperature densification is effective, dehydroxylation adhesion occurs between the particles of the powder, resulting in serious agglomeration of the powder. Although subsequent means such as airflow milling can depolymerize part of the powder, it still cannot reach the original particle size. At the same time, the airflow mill itself will also have a certain destructive effect on the morphology of the spherical powder. Therefore, there is an urgent need in the industry for a method that can improve the agglomeration problem of spherical silica powder after high-temperature densification synthesized by the chemical method. Summary of the Invention

[0004] Aiming at the agglomeration problem between particles caused by high-temperature densification in the prior art, the present invention provides a method for improving the agglomeration of sub-micron silica powder. The present invention uses nano-scale carbon black as a barrier substance to prevent powder agglomeration during high-temperature calcination, thereby obtaining sub-micron spherical silica powder with high true density and monodispersion.

[0005] The technical solution of the present invention is as follows:

[0006] A method for improving the agglomeration of silica powder, comprising the following steps:

[0007] (1) Prepare a mixed slurry containing silica raw powder and carbon black;

[0008] (2) Spray-dry the mixed slurry obtained in step (1).

[0009] (3) Calcinate the powder obtained in step (2) at high temperature in nitrogen to densify the powder, and then cool it.

[0010] (4) Conduct low-temperature carbon removal calcination on the powder obtained in step (3) in air.

[0011] (5) Disperse the powder obtained in step (4) to obtain monodisperse silica powder.

[0012] Preferably, the silica raw powder is a submicron spherical powder synthesized by a chemical method. Among them, the chemical method preferably adopts the sol-gel method, and the particle size range of the silica raw powder is 100 - 900 nm.

[0013] Preferably, in step (1), the carbon black is added in the form of carbon black powder and / or carbon black slurry, wherein the solvent of the carbon black slurry is ethanol or water, and the mass fraction of carbon black in the carbon black slurry is 10 - 60%.

[0014] Preferably, the particle size range of the carbon black is 10 - 70 nm.

[0015] Preferably, in step (1), by mass fraction, the mixed slurry contains 45 - 50% of silica raw powder and 45 - 50% of dispersant, and the mass of carbon black accounts for 2 - 20% of the mass of silica raw powder.

[0016] Preferably, the dispersant is ethanol and / or water.

[0017] Preferably, in step (3), the high-temperature calcination temperature is 900 - 1100 °C, and the calcination time is 1 - 6 h.

[0018] Preferably, in step (4), the low-temperature carbon removal calcination temperature is 500 - 700 °C, and the calcination time is 1 - 10 h.

[0019] Preferably, the dispersion treatment in step (5) is carried out by using a jet mill or a vibrating screen.

[0020] Preferably, the true density of the monodisperse silica powder prepared in step (5) is greater than 2.20 g / cm 3 .

[0021] The beneficial effects of the present invention are as follows:

[0022] (1) After mixing carbon black with silica raw powder in the present invention, the silica raw powder is wrapped. During high-temperature calcination, through nitrogen protection, the carbon black powder is retained and a barrier is formed, which is SiO 2The particles cannot or are not easily adhered to each other, and then decarbonized and calcined at a low temperature. The obtained powder can be further processed by an air sieve or a vibrating sieve to obtain a monodisperse powder;

[0023] (2) The treatment method of the present invention helps to greatly improve the agglomeration phenomenon of silica powder. The present invention uses carbon black as an additive, which is more economical, has less pollutant emissions, is environmentally friendly, and has a lower cost;

[0024] (3) The powder prepared by the present invention needs to be calcined at a high temperature and has a good density. Description of the Drawings

[0025] The present invention will be further described below in conjunction with the drawings and embodiments:

[0026] Figure 1 is the particle size distribution diagram of the powder obtained in Example 1;

[0027] Figure 2 is the particle size distribution diagram of the powder obtained in Example 2;

[0028] Figure 3 is the particle size distribution diagram of the silica raw powder used in Example 1 after conventional sintering treatment;

[0029] Figure 4 is the particle size distribution diagram of the silica raw powder used in Example 2 after conventional sintering treatment. Detailed Embodiments

[0030] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the specific embodiments and with reference to the drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0031] The silica raw powder used in the present invention is preferably silica raw powder prepared by the sol-gel method (also known as the STOBER method). The silica raw powder used in the following examples is self-made, and the specific synthesis process is as follows: A mixed solution of 100 kg of methanol, 30 kg of pure water, and 12 kg of ammonia water (mass fraction 25%) is used as the bottom material. The stirring speed is 300 r / min and the bottom material temperature is controlled at 25°C. At the same time, a mixed solution of 90 kg of methyl orthosilicate and 16 kg of methanol and a mixed solution of 30 kg of pure water and 12 kg of ammonia water (mass fraction 25%) are added dropwise. The dropping time is 1 h. After the dropping is completed, evaporation and concentration are carried out, and drying is carried out to obtain 0.5-μm spherical silica raw powder. Similarly, with other conditions unchanged, when the stirring speed is increased to 400 r / min and the bottom material temperature is controlled at 35°C, 0.3-μm spherical silica raw powder can be obtained.

[0032] Example 1

[0033] 1. Take 5000 g of silica raw powder (average particle size of 0.3 μm) and dissolve it in 5000 g of ethanol. Add 1000 g of carbon black slurry (ethanol solvent, carbon black mass content of 50%), and stir until there are no white spots in the slurry to obtain a mixed slurry;

[0034] 2. Spray-dry the mixed slurry;

[0035] 3. Put the powder obtained in step 2 into an atmosphere furnace. Under a nitrogen environment, slowly heat it up to 990 °C and keep it warm for 2 h. Then, end the program and cool it down to room temperature;

[0036] 4. Put the powder obtained in step 3 into an atmosphere furnace. Under an air environment, slowly heat it up to 600 °C and keep it warm for 4 h. Then, end the program and cool it down to room temperature;

[0037] 5. Jet mill the powder obtained in step 4 to obtain monodisperse silica powder.

[0038] The average particle size of the silica powder obtained in this example is 0.376 μm, the maximum particle size is 0.872 μm, the sphericity is 100%, and the true density is 2.25 g / cm 3 , and the particle size distribution diagram of the powder is as Figure 1 shown.

[0039] The silica raw powder used in this example is subjected to conventional sintering without adding carbon black as a barrier agent. Under an air atmosphere, slowly heat it up to 990 °C and keep it warm for 2 h. The particle size distribution diagram of the silica powder obtained after treatment is as Figure 3 shown. The average particle size of the obtained silica powder is 4.85 μm, the maximum particle size is 308 μm, the sphericity is 100%, and the true density is 2.25 g / cm 3 . By comparison, it can be seen that under the condition that the true density and sphericity remain unchanged, with the same treatment method, the powder after adding the carbon black slurry has been reduced to the initial particle size, while there is still a large amount of agglomeration in the powder obtained by conventional sintering. It can be seen that the treatment method of the present invention helps to improve the agglomeration phenomenon of silica powder.

[0040] Example 2

[0041] 1. Take 5000 g of silica raw powder (average particle size of 0.5 μm) and dissolve it in 5000 g of ethanol. Add 500 g of carbon black slurry (ethanol solvent, carbon black mass content of 50%), and stir until there are no white spots in the slurry to obtain a mixed slurry;

[0042] 2. Spray-dry the mixed slurry;

[0043] 3. Put the powder obtained in Step 2 into an atmosphere furnace. Under a nitrogen environment, slowly heat it up to 995 °C, and keep it at this temperature for 2 h. Then, end the program and cool it down to room temperature.

[0044] 4. Put the powder obtained in Step 3 into an atmosphere furnace. Under an air environment, slowly heat it up to 600 °C, and keep it at this temperature for 4 h. Then, end the program and cool it down to room temperature.

[0045] 5. Pass the powder obtained in Step 4 through a vibrating screen to obtain monodisperse silica powder.

[0046] The average particle size of the silica powder obtained in this example is 0.517 μm, the maximum particle size is 1.13 μm, the sphericity is 100%, and the true density is 2.25 g / cm 3 , and the particle size distribution diagram of the powder is as Figure 2 shown.

[0047] The silica raw powder used in this example is subjected to conventional calcination without adding carbon black as a barrier agent. In an air atmosphere, slowly heat it up to 995 °C, and keep it at this temperature for 2 h. The particle size distribution diagram of the silica powder obtained after treatment is as Figure 4 shown. The average particle size is 14.3 μm, the maximum particle size is 66.8 μm, the sphericity is 100%, and the true density is 2.25 g / cm 3 . It can be seen by comparison that under the condition that the true density and sphericity remain unchanged and with the same treatment method, the powder after adding the carbon black slurry has been reduced to the initial particle size, while there is still a large amount of agglomeration in the powder obtained by conventional sintering. It can be seen that the treatment method of the present invention helps to improve the agglomeration phenomenon of silica powder.

[0048] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundary of the appended claims, or equivalent forms of such scope and boundary.

Claims

1. A method for improving the agglomeration of silica powder, characterized in that, it comprises the following steps: (1) Prepare a mixed slurry containing silica raw powder and carbon black; wherein, the silica raw powder is a sub-micron spherical powder synthesized by a chemical method, and the particle size range of the silica raw powder is 100 - 900 nm; the mass of carbon black accounts for 10 - 20% of the mass of the silica raw powder, and the particle size range of the carbon black is 10 - 70 nm; (2) Spray-dry the mixed slurry obtained in step (1); (3) Calcinate the powder obtained in step (2) at a high temperature in nitrogen, and then cool it; (4) Calcinate the powder obtained in step (3) at a low temperature to remove carbon in air; (5) Disperse the powder obtained in step (4) to obtain monodisperse silica powder.

2. The method for improving the agglomeration of silica powder according to claim 1, characterized in that, in step (1), the carbon black is added in the form of carbon black powder and / or carbon black slurry, wherein the solvent of the carbon black slurry is ethanol or water, and the mass fraction of carbon black in the carbon black slurry is 10 - 60%.

3. The method for improving the agglomeration of silica powder according to claim 1, characterized in that, in step (1), by mass fraction, the mixed slurry contains 45 - 50% of silica raw powder and 45 - 50% of dispersant.

4. The method for improving the agglomeration of silica powder according to claim 3, characterized in that, the dispersant is ethanol and / or water.

5. The method for improving the agglomeration of silica powder according to claim 1, characterized in that, in step (3), the high-temperature calcination temperature is 900 - 1100 °C, and the calcination time is 1 - 6 h.

6. The method for improving the agglomeration of silica powder according to claim 1, characterized in that, in step (4), the low-temperature carbon removal calcination temperature is 500 - 700 °C, and the calcination time is 1 - 10 h.

7. The method for improving the agglomeration of silica powder according to claim 1, characterized in that, the dispersion treatment in step (5) is carried out using a jet mill or a vibrating screen.

8. The method for improving the agglomeration of silica powder according to claim 1, characterized in that, The true density of the monodisperse silica powder obtained in step (5) is greater than 2.20 g / cm 3 .

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